In the rigid pavement industry, concrete failures often occur in isolated areas. In the past, saw-cutting failed slabs in multiple smaller sections and then individually removing these sub-sections separately accomplished removal of these damaged slabs. This has become known as the xe2x80x9cnon-impactxe2x80x9d method of removal. An alternative to this xe2x80x9cnon-impactxe2x80x9d method is known as the xe2x80x9cimpact methodxe2x80x9d in which an air compressor-powered jackhammer mounted on a backhoe is used to xe2x80x9crubble-izexe2x80x9d the damaged slab. This rubble must then be removed, and the underlying base must be repaired before the replacement slab can be installed, costing more time and money. The non-impact method spares the structural integrity of the base layer of the rigid pavement, while the impact method destroys the structural soundness of the base material. The non-impact method is preferred due to the added labor, cost and time of repairing the damaged base material when the impact method is used.
At this point the concrete is placed, finished and cured. Depending on the type of concrete used, curing could require hours to days before reaching design strength and being put back into service. Because the economic cost of stopping vehicular or aircraft traffic, and the inconvenience to the public in shutting down the transportation system, choices had to be made between closing lanes of highways or airport landing fields for long periods of time or, alternatively, using very expensive concrete products which cure in a few hours. These fast setting concretes can be so sensitive and unpredictable that they sometimes set up while still in the transit mix truck; or if certain conditions change slightly they can take 12 hours to set up instead of the usual four to six hours. Another great concern is that if the repair location is more than a short haul distance from a concrete production plant fast-setting concrete mixes were infeasible because of their short set times. One alternative is to set up portable batch plants for on-site preparation of fast-setting concrete, but additional costs are associated with this operation. For these reasons, this method of repair is extremely expensive and problematical.
An alternative to the fast-setting concrete method is to place pre-cast slabs into the holes from which the damaged panels were removed. Then an expanding foam injection process raises the new panel into position. Both methods (fast-setting concrete or pre-cast panels) have saved time, also saving effort, while allowing the repairs to be done in an eight hour shift in the middle of the night, or at a time when the highway, runway, or bridge can be closed or partially shut down. Because of the expense of fabricating and hauling pre-cast panels to the site and using the expensive expanding foam agents, the latter method proved more expensive than using fast-setting concrete but less problematical.
This novel invention solves many of the problems of the prior art methods of removing and replacing damaged rigid pavement sections.
The novelty of this invention is in the way it is used to remove, and replace various rigid pavements, in particular, the concrete used in highways and runways at airports. This invention utilizes an external framing (and thus the present frame may be referred to as an xe2x80x9cExo-Liftxe2x80x9d frame, as in xe2x80x9cexo-skeletalxe2x80x9d), a structural frame to remove broken concrete slabs as single units, and replace the same with new panels. It further acts to externally reinforce the new panels during lifting and aligning in position. It maintains structural support for the replacement slab during its final placement and connection to adjacent slabs, structures, and various other items depending on its application. Support is also maintained while the replacement slab is being bedded and anchored in cementitious or other properly chosen fast-setting materials.
Initially, using a novel tilted guide platform for mounting the concrete saw at a small angle to the perpendicular modifies the saw-cutting process. This allows the concrete joint to be double sawn, once vertically and once at a small angle, to give the concrete slab being removed a beveled edge, which allows it to be removed in a vertical direction without binding to and possibly damaging the rigid concrete pavement to remain. This provides significant savings in time and monetary cost.
After saw cutting around the area to be replaced, the frame is placed over the area of the broken-up concrete. Because it is important to preserve the integrity of the layer just below the concrete layer (which is typically aggregate base, cement treated base, asphalt base, Lean concrete or some similar base material), the broken pieces of slab are individually drilled for anchor installations. The new frame is adjustable both in width and length to accommodate any configuration of cracks in the damaged pavement. Once the frame is bolted to the broken slab, the slab can be removed as a single unit by crane. This saves much time and allows the unit to be hauled off the site and out of the way quickly and efficiently. This frame can save an estimated 10 to 60 percent of the usual time over the current demolition and piecemeal removal methods. The base material is essentially undisturbed, alleviating the need to repair it and thus saving more time and money.
The new frame allows the choice of manufacturing pre-cast replacement panels efficiently at a pre-cast yard. The frame could be attached to these panels at the site of manufacture to facilitate their transportation to the job site. Alternatively, the replacement slabs can be cast at or near the job site. Since the frame reduces the moment loading of the replacement slabs during lifting, transport and installation, it is no longer necessary to include internal steel reinforcement in their manufacture to enable them to withstand the stresses of shipping, lifting, and installation (which are much greater than the stresses encountered during the actual traffic loading of the slab), thus saving time and monetary expense.
Now the slab with the frame attached can be crane-lifted into place, where it is aligned with the pavement surrounding it by the extensions of the longitudinal and transverse beams. The replacement slab will also be supported so that it can leave a small void under the new slab. This void produces the prism for the new base support layer, which can be filled with a very small amount of fast-setting grout. The grout can be mixed at the site with no transit mix trucks required. Only 5 to 10 percent of the original volume of the slab would be required to be replaced with this fast setting material. Because of the small volume of materials required, bagged products would become economically feasible for use. (Bagged products being those whose performance and specifications are documented, proven and generally accepted in the industry as acceptable for use in applications similar to the present application.) The use of these xe2x80x9cbagged productsxe2x80x9d opens the door to remote use of this method where only a small mixing drum is necessary to mix products which have a much higher level of quality control inherent in their production. Costs ranging several orders above the fast setting concrete mixes are still economic and actually preferable because there is no question as to material consistency and the water addition is observable at the site by the inspector. Products do not need to be hauled, so much xe2x80x9chotterxe2x80x9d mixesxe2x80x94those that set much fasterxe2x80x94can be used without problems occurring such as might be encountered with a ready-mix truck hauling over a distance, or a delay occurring in unloading a truck. Such delays sometimes cause the mix to set up in the truck before it gets unloaded. This is known to happen, and it increases costs significantly. It also increases down time, causing major problems for the facility users. When hotter mixes can be used without these problems, lane closure or runway down time can be dramatically reduced. Because the material under the slab would only need to meet a small percentage of the strength of materials which were used to support the surface load, the time before which loading could be allowed would be significantly shortened. Once the grout underlying the new slab reached initial set and achieved adequate compressive strength, the present frame can be unbolted and removed and traffic loading can be resumed.
The grout can be pumped into the low side of the slab edge and will fill upward forcing out air bubbles. As the void below the slab is filled it also fills any irregularities in the base surface providing a uniformly supported replacement slab. As the grout continues to be pumped it rises to fill the voids where the rebar-to-slab splices are, and then finally the joints surrounding the replacement slab are filled to a level just below the surface. Immediately after the initial set the joints can be topped off to be flush with the adjoining surfaces. All that is left is to remove the frame and fill the connection holes with the same grout. Within minutes the replacement slab will be able to accept traffic loading.
The frame is completely collapsible into single beam sections that can typically be lifted, maneuvered and bolted in place by a two-person crew, without the use of equipment. The present frame saves both time and money over the prior art methods.
This frame advances the state of the art and science of removing, manufacturing, transporting, installing, and anchoring of concrete or other composition slabs. This opens the doors to meeting the needs of transportation, on the ground and in the air, assisting engineers in overcoming many of the problems they are facing and those, which shall become much greater. The exo-skeletal novelty opens doors, affecting many applications on virtually all fronts, including, but not limited to: slab construction and materials; transportation; installation methods; novel connection methods; handling; removal; economy; safety; downtime; inter-slab reinforcement (dowelingxe2x80x94load transferring).